/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.nutch.plugin;

import org.apache.hadoop.conf.Configuration;

/**
 * A nutch-plugin is an container for a set of custom logic that provide
 * extensions to the nutch core functionality or another plugin that provides an
 * API for extending. A plugin can provide one or a set of extensions.
 * Extensions are components that can be dynamically installed as a kind of
 * listener to extension points. Extension points are a kind of publisher that
 * provide a API and invoke one or a set of installed extensions.
 * 
 * Each plugin may extend the base <code>Plugin</code>. <code>Plugin</code>
 * instances are used as the point of life cycle managemet of plugin related
 * functionality.
 * 
 * The <code>Plugin</code> will be startuped and shutdown by the nutch plugin
 * management system.
 * 
 * A possible usecase of the <code>Plugin</code> implementation is to create or
 * close a database connection.
 * 
 * @author joa23
 */
public class Plugin {
	private PluginDescriptor fDescriptor;
	protected Configuration conf;

	/**
	 * Constructor
	 * 
	 */
	public Plugin(PluginDescriptor pDescriptor, Configuration conf) {
		setDescriptor(pDescriptor);
		this.conf = conf;
	}

	/**
	 * Will be invoked until plugin start up. Since the nutch-plugin system use
	 * lazy loading the start up is invoked until the first time a extension is
	 * used.
	 * 
	 * @throws PluginRuntimeException
	 *             If the startup was without successs.
	 */
	public void startUp() throws PluginRuntimeException {
	}

	/**
	 * Shutdown the plugin. This happens until nutch will be stopped.
	 * 
	 * @throws PluginRuntimeException
	 *             if a problems occurs until shutdown the plugin.
	 */
	public void shutDown() throws PluginRuntimeException {
	}

	/**
	 * Returns the plugin descriptor
	 * 
	 * @return PluginDescriptor
	 */
	public PluginDescriptor getDescriptor() {
		return fDescriptor;
	}

	/**
	 * @param descriptor
	 *            The descriptor to set
	 */
	private void setDescriptor(PluginDescriptor descriptor) {
		fDescriptor = descriptor;
	}

	protected void finalize() throws Throwable {
		super.finalize();
		shutDown();
	}
}
